diff --git a/addons/purchase/models/account_invoice.py b/addons/purchase/models/account_invoice.py
index 43ffb17dddf..90c86f82d55 100644
--- a/addons/purchase/models/account_invoice.py
+++ b/addons/purchase/models/account_invoice.py
@@ -89,7 +89,9 @@ class AccountInvoice(models.Model):
     def _onchange_currency_id(self):
         if self.currency_id:
             for line in self.invoice_line_ids.filtered(lambda r: r.purchase_line_id):
-                line.price_unit = line.purchase_id.currency_id.with_context(date=self.date_invoice).compute(line.purchase_line_id.price_unit, self.currency_id, round=False)
+                if line.purchase_id.currency_id != self.currency_id:
+                    line.price_unit = line.purchase_id.currency_id.with_context(date=self.date_invoice)\
+                        .compute(line.purchase_line_id.price_unit, self.currency_id, round=False)
 
     @api.onchange('invoice_line_ids')
     def _onchange_origin(self):